Solid-phase extraction and spectrophotometric determination of trace amounts of mercury in natural samples

A sensitive and selective solid phase spectrophotometric method for the determination of trace amounts of inorganic mercury is described. Hg2+ was sorbed on a silica gel-packed column as an Hg2+-N,N'- bis(2-mercaptophenyl)ethanediamide (H2L) complex. The Hg2+ complex was eluted from the column using 7 mL of acetone. Various parameters including pH, column flow rate, and ligand concentration were optimized. The complex was found to obey Beer's law from 2.3 to 73.7 mu g mL(-1) within the optimum range when the preconcentration factor was two. The effective molar absorption coefficient at 523 nm was 1.17 x 10(3) L mol(-1) cm(-1) at 523 nm. The concentration limits in Beer's law dropped from 0.09 to 2.95 mu g mL(-1) within the optimum range when the preconcentration factor was 50. The relative standard deviation at a concentration level of 5 mu g mL(-1) Hg2+ (9 repetitive determinations) was 1.6%. The detection limits are 0.34 mu g mL(-1) and 0.015 mu g mL(-1) when the preconcentration factors are 2 and 50, respectively. The method has been used for routine determination of trace levels of Hg2+ in natural waters. The potential application of this method for the removal of Hg2+ from natural samples (sea water and lake water) spiked with 100 ng mL(-1) of Hg2+ was studied. In order to validate the proposed method, LGC 6156 (harbour sediment extractable metals) was analysed by this method. The results proved that excellent extraction of Hg2+ from both natural water samples was obtained by solid phase extraction using N,M-bis(2-mercaptophenyl) ethanediamide.